'INDUSTRIAL' VERTICAL ILLUMINATION MICROSCOPE

c. 1903

MAKER: Edw. Degen (unsigned)

SERIAL NUMBER: none

MODEL: MICROSCOPE PERFECTIONNÉ

DESCRIPTION:

The instrument arises from a typical 'continental' Y-shaped foot on a single round pillar. The 64 x 55 mm stage has a 17 mm opening. There are two stage clips attached to the stage by lacquered brass screws. A gimbaled 35 mm diameter plano-concave mirror is attached to the swinging tailpiece which swings from a short projection screwed into the bottom surface of the stage. The straight pillar limb continues from the stage directly above the substage pillar. Coarse focus is by straight rack and pinion, the rack machined directly into the main optical tube. The fine focus is typical continental form, with a finely threaded screw acting on the sprung pillar above the stage. There is a second flat mirror attached to an articulating arm supported by a ring around the outer tube housing. This ring is free to rotate around the tube. The main optical tube is small and fixed inside the outer tube which has an oval opening in the front. There is a silvered slightly curved reflector which surrounds the inner optical tube to direct light downward around the objective. The distance from the end of the objective can be varied by sliding this reflector up or down.
The objective has a wide opening, allowing the refected light from to travel down the outer part of the optics of the objective, illuminate the object and then the reflected light off the object takes its vertical path through the central part of the objective into the narrow inner optical tube. The outer part of the lenses then are used to transmit the reflected light to the object while the inner part are used to collect the light from the object. The objective is engraved with the number '1.' The eyepiece is marked '3.' There is no drawtube. The case and dissecting instruments are lacking.

HISTORY

Opaque objects were the earliest specimens examined with microscopes. Initially this was achieved with ambient light falling on the object from the side. Soon this light could be concentrated with the use of supplementary lens known as a 'bullseye' condenser which could be free-standing, or mount on the stage or the optical tube of the microscope itself. These arrangements would by definition provide only oblique lighting.
For even illumination, a more sophisticated method was required.
One clever method was the use of a 'Lieberkuhn', a rounded speculum which surrounded the objective; this functioned to reflect light from behind the object backwards on to its surface, but not through the objective itself. Still later, in the nineteenth century, a 'vertical illuminator' was devised in which light directed into a hole on the side of the tube was reflected down onto the object through the objective, either reflected off a thin piece of glass (usually a coverslip), or through a small prism.
The latter technique had the disadvantage of degrading the image somewhat as the light of the reflected image projected upward either around or through the reflecting mechanism. As magnification increased and focal length decreased, the amount of light that could reach the specimen either via a lieberkuhn, or a vertical illuminator was insufficient. The method provided here was an attempt to place the reflector outside the viewed optical path and is a precursor of modern epi-illumination. The difference between this method and modern epi-illumination is that the modern method uses a very wide objective, and directs light through a ring-shaped optical path that surrounds, but is separate from, the objective; then via a reflective ring surface of glass, light is concentrated as a cone of light upon the specimen. The light then travels to the eye through the objective. The instrument illustrated here then illustrates a transitional method of illumination between vertical and epi-ilumination. In this instrument the outer part of the objective itself is used to project light downward, and the reflected light path uses only the central portion of the same objective.

Degen's company, based in Paris, was apparently founded, it was claimed, by the father in 1865 and by sometime in the early twentieth century, it specialized in photographic lenses, other optical equipment and this specialized industrial microscope for viewing opaque objects. The advertisement for it touts it as a 'special microscope for examination and review' of metals, ceramics, crystals, wood, sugar, etc. The original microscope was supplied in a mahogony case with a handle for a dissecting needle, a trough for liquids, and a scalpel.

The engraving in the ad to the upper left shows an articulated flat mirror attached to one of the two handle pieces used to raise or lower the vertical illuminator mirror, and in addition, a second one attached to the upper body via a ring around the tube as in my example above. In the images to the right, an instrument with the articulation attached to the piece used to raise or lower the mirror is shown, followed by the engraving, and then my example with the articulation attached to the optical tube above. It seems that both types were made, and that the engraving was a combined picture to illustrate both possible variations in the same picture. It would seem unlikely that both would be present on the same instrument at the same time, as this would be reduntant.

I would like to thank Albert Balasse of www.lecompendium.com for allowing me to use his image of his microscope with the articulation attached to the handle of the vertical illuminator.